Type 2 diabetes is a chronic progressive disorder, which results from end-organ resistance to the action of insulin in combination with insufficient insulin secretion from the pancreas. The metabolic abnormalities associated with insulin resistance and secretory defects, in particular the hyperglycemia, lead over the course of years to extensive irreversible damage to multiple organs including heart, blood vessels, kidney, and eye. Currently, nearly 200 million or 2.9% of the world population have type 2 diabetes (World Health Organization, Diabetes Fact Sheet No. 312, January 2011; Wild et al., “Global Prevalence of Diabetes: Estimates for the Year 2000 and Projections for 2030,” Diabetes Care 27(5):1047-1053 (2004)), and its prevalence is rising at an alarmingly fast pace in parallel with the rise in the prevalence of overweight and obesity (World Health Organization, Obesity and Overweight Fact Sheet No. 311, January 2011). Until the end of the 20th century, type 2 diabetes was observed only in adults but what was once known as “adult-onset diabetes” is now also diagnosed in children and adolescents, and this growing incidence can be related to the increase in overweight and obesity among children and adolescents. The prevalence of pre-diabetes, an intermediate metabolic stage between normal glucose homeostasis and diabetes, is even greater than that of type 2 diabetes. Currently, nearly 80 million or 26% of the population in the United States alone have pre-diabetes (Center for Disease Control and Prevention, National Diabetes Fact Sheet 2011), and as such are at high risk for progressing to type 2 diabetes. Type 2 diabetes ranks among the ten leading causes of death worldwide, and the World Health Organization projects that mortality from diabetes (90% of which is type 2) will more than double within the next decade (World Health Organization, Diabetes Fact Sheet No. 312, January 2011). Type 2 diabetes also is a major cause of disability. As a consequence of diabetic retinopathy, about 10% of all patients with diabetes in the world develop severe visual impairment and 2% become blind 15 years into the disease (World Health Organization, Diabetes Fact Sheet N° 312, January 2011). Diabetic neuropathy, which affects up to half of all patients with diabetes worldwide (World Health Organization, Diabetes Fact Sheet No. 312, January 2011), accounts for the majority of nontraumatic lower-limb amputations. Indeed, in its recently published first worldwide report on non-infectious diseases, the World Health Organization considers diabetes, together with other chronic non-infectious diseases like cancer and heart disease, a global economic and social burden, which exceeds that imposed by infectious diseases such as HIV/AIDS.
The current drug therapy for type 2 diabetes is focused on correcting the hyperglycemia in the patients. Although a number of small molecules and biologics with different mechanisms of anti-hyperglycemic action are available for use as mono-therapy or combination therapy, most, if not all of these have limited efficacy, limited tolerability, and significant adverse effects (Moller, “New Drug Targets for Type 2 Diabetes and the Metabolic Syndrome,” Nature 414(6865):821-827 (2001)). For example, treatment with sulfonylureas, glinides, thiazolidinediones, or insulin has been associated with weight gain, which is an undesired effect since overweight is considered a driving force in the pathogenesis of type 2 diabetes. Some of these treatments have also been associated with increased risk of hypoglycemia. A limitation specific to the thiazolidinediones is the potential for adverse cardiovascular effects (DeSouza et al., “Therapeutic Targets to Reduce Cardiovascular Disease in Type 2 Diabetes,” Nat Rev Drug Discov 8(5):361-367 (2009)). A meta-analysis of clinical data on the thiazolidinedione rosiglitazone (Avandia®), which was widely used for the treatment of type 2 diabetes, found that the drug increased the risk of myocardial infarction in patients with type 2 diabetes (Nissen et al., “Effect of Rosiglitazone on the Risk of Myocardial Infarction and Death from Cardiovascular Causes,” N Engl J Med 356(24):2457-2471 (2007)). Of all diabetic complications, cardiovascular disease is the main cause of morbidity and mortality in patients with diabetes (World Health Organization, Diabetes Fact Sheet No. 312, January 2011; Center for Disease Control and Prevention, National Diabetes Fact Sheet 2011), and hence an aggravation of cardiovascular risk by drug treatment is absolutely unacceptable. In the wake of the debate about the cardiovascular safety of thiazolidinediones, the FDA issued a guidance on evaluating cardiovascular risk in new anti-diabetic therapies to treat type 2 diabetes (Opar A, “Diabetes Drugs Pass Cardiovascular Risk Check,” Nat Rev Drug Discov 8(5):343-344 (2009)). Meanwhile, thiazolidinediones lost their popularity. Even for glucagon-like peptide-1 agonists, one of the latest class of drugs introduced for the treatment of type 2 diabetes, concerns about safety have been raised, namely the potential for carcinogenicity (Opar A, “Diabetes Drugs Pass Cardiovascular Risk Check,” Nat Rev Drug Discov 8(5):343-344 (2009)). Therefore, novel therapies that are more effective and safer than existing drugs are needed. Since the currently available drugs do not directly target complications of advanced diabetic disease, especially cardiovascular disease, therapies that are not only effective in lowering blood glucose but also reduce cardiovascular risk factors such as dyslipidemia are particularly desired.
A search conducted by Eli Lilly & Co. for potential novel biotherapeutics to treat type 2 diabetes led to the discovery of fibroblast growth factor (FGF) 21 as a protein that stimulates glucose uptake into adipocytes in an insulin-independent fashion (Kharitonenkov et al., “FGF-21 as a Novel Metabolic Regulator,” J Clin Invest 115(6):1627-1635 (2005)). FGF21 has since emerged as a key endocrine regulator not only of glucose metabolism but also of lipid metabolism, and has become one of the most promising drug candidates for the treatment of type 2 diabetes, obesity, and metabolic syndrome. In mouse models of diabetes and obesity, pharmacologic doses of FGF21 lower plasma glucose and increase insulin sensitivity (Kharitonenkov et al., “FGF-21 as a Novel Metabolic Regulator,” J Clin Invest 115(6):1627-1635 (2005); Coskun et al., “Fibroblast growth factor 21 corrects obesity in mice,” Endocrinology 149(12):6018-6027 (2008)). Concurrently, FGF21 lowers plasma triglyceride and cholesterol, enhances lipolysis and suppresses lipogenesis, and accelerates energy expenditure (Kharitonenkov et al., “FGF-21 as a Novel Metabolic Regulator,” J Clin Invest 115(6):1627-1635 (2005); Coskun et al., “Fibroblast growth factor 21 corrects obesity in mice,” Endocrinology 149(12):6018-6027 (2008)). In obese mice, FGF21 causes weight loss, in lean mice, it is weight neutral (Kharitonenkov et al., “FGF-21 as a Novel Metabolic Regulator,” J Clin Invest 115(6):1627-1635 (2005); Coskun et al., “Fibroblast growth factor 21 corrects obesity in mice,” Endocrinology 149(12):6018-6027 (2008)). Thus, FGF21 has some of the most desired characteristics of a drug for the treatment of type 2 diabetes; not only does it improve glycemic control, but also directly affects cardiovascular risk factors, such as hypertriglyceridemia, and reduces obesity, which is considered the single most important promoter of type 2 diabetes. Importantly, FGF21 does not induce hypoglycemia (Kharitonenkov et al., “FGF-21 as a Novel Metabolic Regulator,” J Clin Invest 115(6):1627-1635 (2005)), a side effect that can occur with several of the current anti-diabetic therapies, including insulin. Moreover, FGF21 does not exhibit any mitogenic activity in mice (Kharitonenkov et al., “FGF-21 as a Novel Metabolic Regulator,” J Clin Invest 115(6):1627-1635 (2005)), ruling out the possibility of a carcinogenic risk. The findings on FGF21 therapy in mouse models of diabetes have been reproduced in diabetic rhesus monkeys (Kharitonenkov et al., “The Metabolic State of Diabetic Monkeys is Regulated by Fibroblast Growth Factor-21,” Endocrinology 148(2):774-781 (2007)), and are currently followed up with clinical trials in humans (Kharitonenkov et al., “FGF21 Reloaded: Challenges of a Rapidly Growing Field,” Trends Endocrinol Metab 22(3):81-86 (2011)). However, there is a need for more effective FGF21 therapeutics.
The present invention overcomes these and other deficiencies in the art.